COOPERATIVE EFFECTS IN BLUE-LIGHT EMISSION OF POLY-(PARA-PHENYLENE)-TYPE LADDERPOLYMER

A hyperlinear increase of radiative quantum efficiencies of poly (para -phenylene)-type ladderpolymer in the blue-green region as a function of subpicosecond excitation intensity is reported. The light emission in the range from 485 to 495 nm undergoes a change from linear behavio r to a second order response; the two regimes are separated by a disti nct threshold of 3.1 mJ/cm(2). Above this threshold, investigation by femtosecond excitation-correlation measurements indicate that the hype rlinear blue emission is associated with a characteristic excitonic de population of 2 ps. (C) 1997 American Institute of Physics. [S0003-695 1(97)00645-1].